It is well known by those skilled in the art that the control of stresses in thin films on substrates is critical for the conductivity, mechanical stability, and performance of semiconductor devices.
The problems with stresses, tensile and compressive, in thin films results from the mismatch between the thin film and substrate materials which cannot usually be modified and from the stresses that are created in the thin film by overlying dielectric films.
The presence of tensile stresses in the thin film may cause rupture and/or peeling of mechanically fragile films, for example chromium. In addition, tensile stresses have been shown to cause stress-voiding and rupture of thin film conductors. For example, interconnection lines formed on semiconductor substrates to interconnect different semiconductor devices may form voids which extend all the way across interconnection lines, causing open-circuit failure or notches may form at the edges of the interconnection lines causing partial loss of a cross sectional area, resulting in early electromigration failure.
Mechanically weak films may also undergo morphological modifications such as hillock growth because of the compressive stresses developed under heating and/or cooling cycles during the fabrication of the substrate on which the thin film has been formed.
One method of controlling stresses in thin films known by those skilled in the art is to use ion bombardment either during evaporation-condensation, or during sputtering (bias sputtering) when forming the thin film. This technique allows a compressive stress component to be added to the other stresses present in the thin film. Another solution to control the stresses in thin films has been to add gaseous impurities, for example, oxygen, to the thin film to introduce a compressive stress component. These gaseous impurities are added to the thin films using reactive evaporation or sputtering.